Urbanization reduces evapotranspiration and alters its components across 20 global urban forests

Urban woodland evapotranspiration (ET) is a key variable in the water cycle of the urban Earth Critical Zone (ECZ). However, the specific impacts of urbanization on ET and its individual components, include canopy interception (I), soil evaporation (E) and vegetation transpiration (T), within urban woodlands have remained largely unquantified. This study employed a hybrid modeling framework that integrates three source physical process-based modeling with machine learning to evaluate the long-term dynamics of ET components (interception, evaporation, and transpiration) and their key driving factors across urban forests in 20 global cities. The results demonstrate that the proposed model accurately simulates ET in urban forests, achieving an average root-mean-square-error (RMSE) of 34.8 W/m 2 . Over the nearly four-decade period, total ET and its components exhibited a significant decreasing trend, with average annual declines of 1.46 mm for ET, 1.18 mm for T, 0.23 mm for E, and 0.05 mm for I. Shapley Additive Explanations (SHAP)-based attribution analysis indicated that the reduction in urban forest cover driven by urban expansion was the primary factor contributing to the decline in ET and its components (interception, evaporation, and transpiration) in urban forests. While the urban heat island effect increased atmospheric evaporative demand, the biophysical limitations imposed by vegetation loss had a far greater impact. These findings underscore the necessity of expanding urban forested areas to enhance their ET cooling services. This strategy is critical for mitigating the negative effects of climate change on the urban ECZ and improving ecological resilience. • Combination of machine learning with three source process-based models for estimating evapotranspiration (ET) and its components in urban forests. • Both canopy interception (I), soil evaporation (E) and vegetation transpiration (T) in urban forests exhibited a significant downward trend with urbanization. • The decline in ET and its components in urban forests is primarily attributable to the reduction of forest cover driven by urban expansion.